Modulation-controlled magnetron oscillator



y 1937. w H. E. HOLLMANN 2,080,571

MODULATION CONTROLLED MAG NETRON OSCILLATOR Fiied Aug. 15, 1935INVENTOR. HANS ERICH HOLLMANN BY 7%. v-W

ATTORNEY.

Patented May 18, 1937 UNITED ST T OFFICE signor to TelefunkenGesellschaft fiir Drahtlose Telegraphic m. b. H., Berlin, Germany, acorporation of Germany Application August 15, 1935, Serial No. 36,308 InGermany August 21, 1934 3 Claims.

This invention relates to magnetron oscillators and has particularly todo with the provision of improved means for modulating ultra-highfrequency oscillators.

The magnetron, as is known, is extremely well suited for producingultra-short waves, and especially favorable useful eifects are obtainedtherewith where the anode cylinder is divided into two or severalsegments. In a simple magnetron, modulation fluctuations may besuperposed on the direct plate potential. In the case of a split anodemagnetron with two segments, or in case of a magnetron having aplurality of splits in the anode and two groups of segments, connectedin both cases to the two poles of a resonance system, there is obtaineda more favorable stabilization of the modulation characteristic and agreater range of control, if the two segments or the two groups ofsegments instead of being modulated in equal phase, are modulated inpush-pull. This was hitherto done in such a manner that two modulationvoltages with a phase displacement of 180 such as furnished for instanceby a push-pull transformer, were superposed on the equal potentialsapplied to the two segments, or groups of segments respectively.

This hitherto known method of modulation implies all the disadvantagesencountered in the direct anode potential modulation of any transmitter.Moreover, these secondary windings of the push-pull transformer arehighly loaded by the inner resistances of the magnetron, thus requiringconsiderable modulation energies to produce the alternating potentialsnecessary for full control of the magnetron. A further drawback is to beseen in the fact that the secondary windings must carry a considerabledirect current load to the anode. Hence a transformer of largedimensions is necessary, otherwise the ohmic resistance loss would beexcessive.

It is an object of my invention to avoid the above mentioned drawbacksby providing means including electron discharge tubes interposed in theanode circuit of a magnetron oscillator through the medium of whichmodulation may be effected.

In carrying out my invention I have found it preferable to place inparallel with each branch of the anode circuit of a magnetron oscillatoran electronic path whereby approximately the same load is carried as inthe generator tube. A common load for the anode circuits of themagnetron and for the parallel circuits thus introduced may be appliedin series with a source of direct current potential between the cathodeand the anodes of the magnetron. In modulating the magnetron,oscillations from any suitable modulating source may be applied to thecontrol electrodes of the parallel tubes. The dissipation of power inthe modulating circuits may then be kept within 5 negligibly smallamounts due to the fact that only grid control energy is necessary.

The sole figure of the drawing illustrates diagrammatically a preferredembodiment of my invention.

Referring to the diagram I show a magnetron type of electron dischargetube M having a cylindrical arrangement of split anodes S1 and S2. Thefilament cathode is shown as a small circle centrally disposed withrespect to the cylindrical system of anodes. It will be understood thatthe cathode has two terminals in order that a source of potential may beapplied thereto for heating the same. This, however, has not been shownin the drawing because it is well understood by those skilled in theart.

Each of the anode sectors S1 and S2 may be fed with direct current anodepotential from any suitable source (not shown) to be inserted betweenthe terminals +Ea and -Ea. In the cir- 5 cui't leads to the anodes,choke coils W1 and W2 are preferably provided. These chokes wouldnaturally have iron cores if audio frequency modulation is to be used.The anode leads themselves are shown as a Lecher-wire system, which maybe tuned to the desired frequency of a carrier wave by means of acapacitor C, the terminals of which may be bridged across theLecher-wire system at suitable points relative to the location ofvoltage nodes along the transmission wires.

Each of the anode circuit leads of the magnetron is branched to anoutput circuit of an electron discharge tube such as R1 and R2. Thesetubes may be operated in a push-pull manher by connecting the grids toopposite terminals of a secondary winding of a transformer T. Thistransformer secondary has a mid-tap connecting through a gridbiasbattery 3 to the cathodes of the respective tubes R1 and R2, and of themagnetron tube M.

When modulations are applied to the primary winding of the transformer Tit will be clearly seen that the tubes R1 and R2 will be controlled in apush-pull manner. Each tube will carry half of the current to be used inmodulating the 5 magnetron since the variation in load which iscontrolled by one of the modulating tubes afiects only that half of thedissipation of the anode energy in the magnetron which is applied to oneof the anode segments.

If desired, the two sides of the magnetron tube may be fed with energyfrom respectively independent sources. Such an arrangement provides forindependent setting of the working points in the two modulationcharacteristics as applied to the two anode segments S1 and S2.Substantially the same results may be obtained, however, by placing asuitable ohmic resistor in one or in both of the circuit leads to theanode segments of the magnetron. In this manner the effective platepotential will be decreased by the voltage drop through the resistors.Such resistors should preferably be bridged by suitable capacitors inorder to prevent alternating voltages across the resistors fromdisturbing the uniform push-pull modulation.

In the operation of my invention it will be seen that I have provided ameans for controlling a magnetron oscillator through a transformer T ofrelatively small proportions. The push-pull manner of control as appliedto the anode sections S1 and S2 has decided advantages over such controlas might be applied to the cylindrical anode structure of a magnetronnot having split segments. Other advantages of the invention will alsobe aparent to those skilled in the art.

It is to be understood that various modifications of my invention may beutilized without de-- parting from the spirit and scope thereof asdefined by the appended claims.

I claim:

1. In an ultra-high frequency oscillator, a magnetron discharge tubehaving a cathode and a plurality of anode sectors, a source of directcurrent in circuit between the cathode and each of the anode sectors,means for modulating said oscillator comprising a push-pull networkhaving a pair of electron discharge tubes the output circuits of whichare connected each respectively with one of the anode. sectors of saidmagnetron tube, a source of modulations, and means including atransformer having a secondary winding with a mid-tap connected to thecathode of said magnetron tube and with the extremities of said windingconnected respectively to the grids of said electron discharge tubes,said means being adapted to apply modulating potentials from said source;of modulations to said grids, thereby to control the impedances of saidelectron discharge tubes in a push-pull manner and hence to vary theanode potentials applied to the anode sectors of said magnetron tube.

2. In an ultra-high frequency circuit arrangement, a magnetronoscillator tube having a cathode and a plurality of anode sectors, aLecherwire tuning system having parallel conductors connected to saidanode sectors, a source of direct current potential connected betweenthe cathode and said tuning system, a source of modulating energy, apush-pull transformer having a primary winding connected to saidmodulating source and a secondary winding on which there is a mid-tapconnected to the cathode of said oscillator tube, and a push-pullnetwork having two electron discharge tubes the input circuits of whichinclude respectively different portions of said transformer secondarywinding, and the output circuits of which are disposed in parallelrespectively with different ones of said parallel conductors of saidLecher-wire system.

3. A device in accordance with claim 2 and further characterized in thata capacitive bridge is provided across the. parallel conductors of saidLecher-wire system.

HANS ERICH HOLLMANN.

